EP3812280A1

EP3812280A1 - Tanker aircraft comprising a referencing system

Info

Publication number: EP3812280A1
Application number: EP19382923.1A
Authority: EP
Inventors: Martín Espinosa Sánchez; Javier Valdeolmos Traba
Original assignee: Airbus Defence and Space SA
Current assignee: Airbus Defence and Space SA
Priority date: 2019-10-23
Filing date: 2019-10-23
Publication date: 2021-04-28
Anticipated expiration: 2039-10-23
Also published as: US20210122486A1; US11591104B2; ES2925650T3; EP3812280B1

Abstract

The present invention defines a referencing system for assisting a receiver aircraft in relative positioning during in-flight refueling operation. In particular, this referencing system comprises an array of references congregated on a spot of the tanker aircraft, wherein the array of references provide a distinguishable visual indicator depending on the sector where the receiver aircraft positions.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention belongs to the field of aerial or air-to-air refuelling operations (so-called 'in-flight refuelling'), and particularly it relates to a referencing system for assisting a receiver aircraft in relative positioning during in-flight refueling operation.
To that end, and according to the present invention, the receiver aircraft solely needs to attend to a spot of the rear part of the tanker aircraft.
Further, the present referencing system accounts for the in-flight parameters of the tanker aircraft as well as refuelling operation parameters. In embodiments, these parameters are known beforehand -prior flight- and the referencing system is adjusted before taking-off entailing a passive system in-flight, thus minimizing certification procedures.
The present invention focuses on readily references for the receiver aircraft in order to be suitably positioned, especially during disconnection phase, as the drogue, driven by the surrounding forces, returns to the equilibrium state (so-called nominal position) arising, for instance, contact with the receiver aircraft if the hose is whipped by tension releasing or even incorrect vertical positioning.

BACKGROUND OF THE INVENTION

In refueling operations, a tanker aircraft stores fuel which, via a hose and drogue system, is transferred in-flight to another aircraft -the receiver- which receives it through its probe.
Basically, hose and drogue refueling systems comprise a drum configured to wind/unwind the hose during the refueling operation. This drum is normally further equipped with a fuel pipe connected to a fuel line in connection with a fuel tank, in order to allow this fuel to pass through.
Furthermore, a coupling and a drogue are installed at the end of such hose. On one hand, the coupling has the function of connecting with the receiver aircraft probe and includes a valve for the fuel system.
On the other hand, the drogue has the function of generating the aerodynamic drag necessary to trail and stabilize the hose and to hold the coupling allowing that the receiver pushes forward on the coupling to connect with the tanker.
Different drogues can be used depending on the application, within the typical range 105-325 knots, i.e. around 195-602 km/h. In any scenario, these drogues provide a drag force up to typically 600 Ibf, i.e. around 2.7 kN.
During this aerial refueling, for safety reasons, special attention should be drawn to keep a correct relative position between both aircrafts (tanker and receiver). Otherwise, collision could take place whether during hose deployment with the receiver, during disconnection due to hose over-tension, or even between aircrafts.
Conventionally, two solutions have been typically applied to keep a correct relative position. On one hand, the hose may incorporate marks to estimate the deployed length and, therefore, the distance between both aircrafts. On the other hand, a device fitted around the hose tunnel outlet similarly gives a discrete indication of the hose length.
The pilot of the receiver aircraft is responsible for keeping the actual separation between tanker and receiver normally based on taking visual references over any part of the tanker such as the horizontal stabilizer or the wing. Depending on the receiver model (having the probe above or below pilot vision level) and its location in relation to the tanker, these visual references might be inefficient.
As mentioned, during probe contact with the hose and drogue system, normally only longitudinal indications (based on hose length) are indeed measured while lateral and vertical relative distances are minded by receiver aircraft pilot simply by visual references over the tanker aircraft.
This referencing protocol suffices before contact as the aircrafts are not bind to each other, and even when connected as there is no risk for the hose to freely move. Nevertheless, the relative position becomes especially important during disconnection phase, as the hose releases tension forces and the drogue returns to its free flying position.
The drogue may hit the receiver aircraft if the relative position is far from the nominal position. The nominal position is defined as that position of the hose and drogue system in which there is a force equilibrium in free flying, accounting inter alia for weight (dependent on hose length), hose tension, drogue drag (dependent on tanker speed), etc.
This case is of especial importance in helicopter refueling -having the probe beneath-, as the drogue may fly back near the rotor blades.
Accordingly, there is a need for suitably referencing tanker-receiver aircraft couples providing satisfactory safety levels for all aircraft operational conditions.

SUMMARY OF THE INVENTION

The present invention provides a solution for the aforementioned problems, by a tanker aircraft comprising a referencing system according to claim 1, a method for assisting on relative positioning a receiver aircraft during in-flight refueling operation according to claim 12, and a method for uncoupling the hose and drogue system of a tanker aircraft according to claim 15. In dependent claims, preferred embodiments of the invention are defined.
In a first inventive aspect, the invention provides a tanker aircraft comprising a referencing system for relative positioning a receiver aircraft during in-flight refueling operation via a hose and drogue system,
wherein the referencing system comprises an array of references congregated on a spot of the rear part of the tanker aircraft, preferably of the tail cone thereof,
wherein the array of references defines a plurality of sectors originated from the spot, a sector being defined by its amplitude in angle, wherein,
for each one of these sectors, the array of references is configured to provide a distinguishable visual indicator, and
the array of references being adjustable with respect to:

at least one flight parameter of the tanker aircraft, and
at least one in-flight refueling operation parameter.

The referencing system according to the present invention provides a plurality of sectors in terms of 'spherical sectors' establishing regions of space. Each of these sectors is defined by two radii separated there between by its amplitude in angle (i.e. a circular sector).
Although a spherical sector may be formed, it is of special relevance for the present invention the circular sector formed, as it defines upper and lower boundaries (i.e. two radii) for vertical relative referencing.
In geometry, a sector (or circular sector) is further defined by an arc, thus establishing an area together with the radii. Nevertheless, herein, the arc may be established by the hose length during refuelling as it is the relative longitudinal distance between aircrafts when coupled.
Without prejudice of the visual capacity of the pilots, the array of references are visually distinguishable by associated indicators in each one of these sectors at least up to the hose maximum length. Since the array of references may provide a distinguishable visual indicator beyond such longitudinal distance of the hose length, it is up to the receiver aircraft pilot to distinguish the visual indicators between them even at greater distances, for instance, based on his visual acuity, field of vision, twilight vision, glare, etc.
Therefore, from the spot of the tanker aircraft the plurality of sectors are defined by their amplitude in angle. Accordingly, the receiver aircraft passes through these sectors as it passes through different relative altitudes. In addition, for instance, two sectors may partially overlap thus defining a third sector as within the intermediate area (overlapping area) the array of references provides another distinguishable visual indicator which is the distinguishable visual indicators of each former two sectors at the same time.
Hence, the present invention creates a vertical reference to the receiver aircraft, so the receiver aircraft can determine, especially at the time of disconnection, if it is above or below the nominal position.
Since this nominal position of the hose and drogue system highly depends on flight parameters, in-flight refueling operation parameter, such array of references need to be adjusted with respect to them in order to correctly establish this nominal position.
Therefore, unlike lateral (or even longitudinal) relative positioning, a fixed reference (e.g. based on visual references over disparate areas or the aircraft) cannot be used to ensure the correct vertical position.
Other parameters such as the probe location (addressed in the first inventive aspect within the in-flight refueling operation parameter) on the receiver aircraft highly influences the desired vertical positioning in regard of the nominal position of the system.
It is to be noted that throughout the entire description, the receiver aircraft should be understood as any aviation vehicle able to be supported on air and including any 'fixed-wing' and 'rotary-wing' (so-called helicopters) types.
In a particular embodiment, the spot of the rear part of the tanker aircraft that is preferably of the tail cone thereof is arranged close to a hose outlet tunnel.
Further, in a preferred embodiment wherein the tanker aircraft comprises a cargo ramp, the spot is arranged on said cargo ramp of the tanker aircraft, this cargo ramp being part of the rear part of the tanker aircraft. In further embodiments, this spot is arranged on the dedicated lateral fairings of the cargo ramp in order not to intercede any other equipment.
In a preferred embodiment, the at least one flight parameter of the tanker aircraft comprises:

tanker aircraft speed, and/or
its angle of attack.

Both parameters affect lifting forces of the tanker aircraft and, therefore, modify the surrounding air left behind where the drogue flies.
In a preferred embodiment, the in-flight refueling operation parameter comprises the type of receiver aircraft to be refueled, the sort of drogue, and/or the length of the hose.
That is, the adjustment accounts on one hand for the actual characteristics of the hose and drogue system, and on the other hand, for the actual dimension of aircraft receiver parts along with the probe location and dimension in order to avoid any collision if receiver aircraft shifts from desired (dependent on nominal position of hose and drogue system) during disconnection.
In a particular embodiment, the array of references of the referencing system comprises an array of lights with n light sources, n being a natural number greater than or equal to 3. Preferably, n is 6, that is, the referencing system comprises 6 light sources.
Each light source provides distinguishable visual indicators by projecting light in a sector defined by a predetermined amplitude of projection set by a projection orientation (α_n ), the array of lights being adjustable at least in amplitude (β_n ) and projection orientation (α_n ).
That is, each of these lights, based on their amplitude (β_n ) (i.e. the amplitude in angle) and projection orientation (α_n ), provides a light beam corresponding to a sector. As each of these light sources illuminates a particular sector, it is distinguishable from the other.
In a preferred embodiment, these light sources congregated on the spot of the rear part of the tanker aircraft are arranged aligned. Advantageously, this stresses the fact of being distinguishable from each other.
In an embodiment wherein the tanker aircraft comprises a cargo ramp, the spot may be arranged on said cargo ramp such that the lights sources are visible when the cargo ramp is closed. At this configuration of closed ramp, there is a reduced available space for arranging such a referencing system.
As it was mentioned above regarding the sector overlapping, in a particular embodiment, the light projected by at least two of the n light sources are configured to partially overlap in the respective sectors, these at least two sources of light becoming visible at the same time only within the overlapped sectors.
Therefore, the overlap of two lights imply the generation of a new illuminated sector since light sources congregated on the spot are perceived differently (these two lights simultaneously on) by the receiver aircraft.
In a particular embodiment, the partial overlap establishes a referencing protocol for assisting the receiver aircraft with its relative positioning during the in-flight refueling operation.
This referencing protocol is based on, since the pilot of the receiver aircraft needs only to look at the spot of the tanker aircraft, the array of references therein provides a particular visual indicator able to be distinguishable depending on the sector where the receiver is positioned.
In other words, as the receiver aircraft moves up or down in relation to the nominal height of the hose and drogue system, the pilot of the receiver aircraft timely receives information about his relative position with regard to the tanker aircraft which assist him during this refueling operation. This information is acknowledged by the pilot because, for each height that the referencing system is adjusted to, the pilot perceives the associated visual indicator differently. Knowing beforehand this referencing protocol allows the receiver aircraft pilot to work under a fail-safe protocol.
The sector overlapping features provides a fine tune of this referencing protocol emphasizing the fail-safe characteristics.
In a particular embodiment, the n light sources are at least 3 lights, each one emitting light in any of at least two color tones.
In a preferred embodiment, at least one light source emits red light, while at least another light source emits white light. That is, the array of lights are perceived in its entirety by the receiver aircraft as if it were changing from red to white, and vice-versa, if the receiver moves downwards or upwards, respectively.
Advantageously, the light code is alike the one used in airport approach systems so pilots are accustomed to it. The colour change is based on a combination of lens mounted on different angles and, therefore, it is a passive system.
In a particular embodiment, each sector has an amplitude between 2 to 4° in angle, preferably between 2.5 and 3.5° in angle.
Further, in a preferred embodiment, the projection orientation (α_n ) of each light source is gradually displaced 2° in angle.
The configuration of this embodiment provides a preferred referencing system for helicopters.
In a particular embodiment, the array of references of the referencing system comprises an array of n marks, n being a natural number greater than or equal to 3, and a pointer device distanced from the marks,
wherein each mark provides a distinguishable visual indicator in cooperation with the pointer device for a different sector in such a way that the pointer device visually intervenes a different mark on the spot for a different sector.
In other words, this embodiment uses visual perspective of the receiver aircraft pilot since the pointer device visually intervenes a different mark on the spot depending on the particular sector where receiver aircraft is positioned.
Between the pointer device and the reference marks there is a predetermined longitudinal distance, so that the projection of the reference line with respect to the mark references plane changes depending on the vertical position of the receiver.
It is to be noted that the present embodiment is of special interest when the refueling operation is expected to be accomplished with the cargo ramp opened.
In a particular embodiment, the array of references are adjustable by changing the distance of the pointer device from the marks.
In a preferred embodiment, the array of n marks on the spot are stacked horizontal lines of different color tones.
Therefore, this provides an optimum referencing system for vertical positioning.
These marks may be painted, illuminated or be lights to improve their visibility. In a preferred embodiment, the horizontal lines are either LED or Infrared red lights.
For instance, IR lights enables the pilot of the receiver aircraft to visually determine and locate the stacked horizontal lines during night-time or low visibility conditions enhancing their situational awareness and increasing aircraft operational envelope.
Specifically, these IR lights may be only perceivable through a night-vision device such as night-vision goggles.
In a second inventive aspect, the invention provides a method for assisting on relative positioning a receiver aircraft during in-flight refueling operation of tanker aircraft according to any of the embodiments of the first inventive aspect, wherein the array of references of the tanker aircraft has been previously adjusted with respect to at least one flight parameter thereof, and at least one in-flight refueling operation parameter;
wherein the method comprises the following steps:

a) deploying the hose and drogue system by the tanker aircraft during the in-flight refueling operation, and
b) detecting by the tanker aircraft that a probe of a receiver aircraft to be refueled is coupled, saving the sector from the spot at which the coupling occurs.

That is, before the tanker aircraft takes off, it is known beforehand decisive parameters at which the refueling maneuver is desirable to take place so that both aircrafts are prepared therefor.
Because aircraft industry is highly regulated, refueling operation envelope for couples of tanker and receiver aircrafts should comply with airworthiness certified ones. Therefore, the in situ in-flight refueling conditions are tailored to the expected ones.
Advantageously, this strongly minimizes certification regulations as the referencing system according to the invention acts as a passive system already adjusted on-ground. The lack of electronics or digital involvement entails less risk exposure.
Under some circumstances, the referencing system when incorporated into a tanker aircraft according to the present invention may be understood as a non-certifiable system.
In a particular embodiment, the tanker aircraft is according to any one of the embodiments where the referencing system comprises an array of lights with n light sources, and
the array of references of the tanker aircraft has been previously adjusted on-ground so that the adjustment of the distinguishable visual indicators comprises projecting light from the n sources of light in sectors, further adjusting their predetermined projection amplitude and projection orientation (α_n ) based on the at least one flight parameter of the tanker aircraft during the following in-flight refueling operation, and at least one in-flight refueling operation parameter.
In a particular embodiment, the tanker aircraft comprises a referencing system based on an array of n marks, n being a natural number greater than or equal to 3, and a pointer device distanced from such marks, and
the array of references of the tanker aircraft has been previously adjusted on-ground so that the adjustment of the distinguishable visual indicators comprises changing the distance of the pointer device from the marks based on the at least one flight parameter of the tanker aircraft during the following in-flight refueling operation, and at least one in-flight refueling operation parameter.
In a third inventive aspect, the invention provides a method for uncoupling the hose and drogue system of a tanker aircraft according to any one of the embodiments of the first inventive aspect from a probe of a receiver aircraft during in-flight refueling operation;
wherein the referencing system defines at least 3 sectors corresponding with different altitudes of the receiver aircraft during the in-flight refueling operation, the at least 3 sectors categorized as upper, suitable, and lower sectors, respectively, and wherein at the suitable sector, the tension of the deployed hose is minimum;
wherein the method comprises:

i. positioning the receiver aircraft within the suitable sector, and
ii. uncoupling the hose and drogue system by the tanker aircraft from the probe of the receiver aircraft.

As it was mentioned, the uncoupling phase is crucial in refueling operation because the drogue (connected to the hose) is released from the probe (further released from this joining force induced by the probe) and it may return to another position driven by the pursuit of equilibrium forces.
In other words, at the suitable sector, the hose and drogue system is at the nominal position. In this position the tension of the deployed hose is minimum since it does not need to counteract for the probe induced tension.
This suitable sector may be either a specific height relative to the tanker aircraft or a range thereof where the return of the hose may not bring into contact with parts of the receiver aircraft.
In a fourth inventive aspect, the invention provides a method for in-flight refueling operation between a tanker aircraft according to any one of the embodiments according to the first inventive aspect and a receiver aircraft, the method comprising the following steps:

assisting on relative positioning a receiver aircraft during in-flight refueling operation of tanker aircraft according to any of the embodiments of the second inventive aspect;
upon connecting the coupling of the drogue of the tanker aircraft to the probe of the receiver aircraft, transferring fuel therebetween;
uncoupling the hose and drogue system of a tanker aircraft according to the third inventive aspect.

All the features described in this specification (including the claims, description and drawings) and/or all the steps of the described method can be combined in any combination, with the exception of combinations of such mutually exclusive features and/or steps.

DESCRIPTION OF THE DRAWINGS

These and other characteristics and advantages of the invention will become clearly understood in view of the detailed description of the invention which becomes apparent from a preferred embodiment of the invention, given just as an example and not being limited thereto, with reference to the drawings.

Figure 1: This figure shows a schematic depict of a plurality of sectors defined from a referencing system according to an embodiment of the present invention.
Figure 2: This figure shows a schematic lateral view of a first embodiment of the distinguishable visual indicators provided by the array of references of the present referencing system according to the present invention.
Figures 3a-3c: These figures show the congregated array of references within the spot of a referencing system according to the first embodiment of the present invention. In addition, it is seen the gradual change of the distinguishable visual indicators as the receiver aircraft moves up or down, respectively.
Figure 4: This figure shows a schematic perspective view of a second embodiment of the array of references, formed by an array of n marks and a pointer device, of the present referencing system according to the present invention.
Figures 5a-5c: These figures show the congregated array of references within the spot of a referencing system according to the second embodiment of the present invention. In addition, it is seen the gradual change of the distinguishable visual indicators as the receiver aircraft moves up or down, respectively.
Figure 6: This figure shows a schematic lateral view of a receiver aircraft close to a tanker aircraft taken as a reference for adjusting the parameters sizing the referencing system from the nominal position of the hose and drogue system according to an embodiment of the present invention.
Figure 7: This figure shows a referencing system located in the rear part of a tanker aircraft according to an embodiment of the present invention.
Figure 8: This figure shows a referencing system of light sources according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The person skilled in the art may recognize that aspects defined herein may be embodied as a referencing system or as a method steps.
Figure 1 depicts a schematic plurality of sectors (4) according to the present invention. The referencing system (1), through distinguishable visual indicators, is in charge of relative positioning a receiver aircraft during in-flight refuelling operation.
The referencing system (1) according to the present invention comprises an array of references congregated on a spot (3) of the rear part of the tanker aircraft, preferably of the tail cone thereof. From this spot (3) the plurality of sectors (4) are originated, wherein each sector (4) is defined by its amplitude in angle (β_n ), and wherein for each sector (4), the array of references is configured to provide a distinguishable visual indicator. The array of references being further adjustable with respect to the at least on flight parameter of the tanker aircraft and at least one in-flight refuelling operation parameter.
As explained above, it provides a simple, quantifiable and non-certifiable referencing system emphasizing safety of in-flight refuelling operation.
In particular, figure 1 shows three sectors (4) originated on a spot (3) of the reference system (1). Each sector (4) provides a distinguishable visual indicator for the receiver aircraft during in-flight refueling operation. Further, each sector (4) is defined by its amplitude angle (β_n ) and the corresponding projection orientation (α_n ).
The two variables depend on the in-flight refuelling operation parameters together with the tanker flight parameters so that, when these are fixed (for instance, based on certification rules) the referencing system is tailored -i.e. adjusted- to that conditions.
As it was mentioned before, this adjustment is necessary for sizing the overall referencing system from the nominal position -i.e. equilibrium forces- of the hose and drogue system in order not to abruptly shifts upon disconnection jeopardizing the integrity of the aircrafts involved in the manoeuvre.
Particularly, to suit the vertical displacement of the receiver aircraft during this refuelling operation, the projection orientation (α_n ) is gradually increased, preferably by 2° in angle. So that, in this vertical displacement, the receiver aircraft pilot shall appreciate or perceive a gradual change of the array of references only looking at the spot where they are congregated.
On the other hand, the amplitude in angle (β_n ) of each of these the sectors (4) (measured around the projection orientation (α_n ), that is, with the latter as a baseline), whether constant or variable through the sectors, establishes the vertical height at which that distinguishable visual indicator will be indeed appreciated during the vertical displacement.
As one skilled in the art may recognize, if the amplitude in angle (β_n ) be greater than the relative angle between two projection orientations (α_n ), the corresponding sectors will overlap at least in part.
Referring back to figure 1, each one of the three sectors (4) provides a distinguishable visual indicator for the receiver aircraft approaching to the tanker aircraft so that, depending on the relative position in which the receiver aircraft is located, it will be within the region defined by one of these sectors. That is, each sector (4) provides a visual information for the receiver aircraft about if the receiver aircraft is indeed in a good region for refuelling operation conditions or not.
In particular, a first sector (4.1) and a third sector (4.3) define a first region and a third region, respectively. If the receiver aircraft is in one of the first and third regions, it would not be in appropriate conditions for the refuelling operation, or even for disconnecting the probe. In contrast, if the receiver aircraft is located in a second region defined by a second sector (4.2) then it would be in the appropriate conditions for the refuelling operation, as the hose and drogue system is located close enough to the nominal position.
That is, if the receiver aircraft is positioned in the first sector (4.1) it is understood that the receiver aircraft is located above the appropriate region for the refuelling operation corresponding to the second sector (4.2); and if the receiver aircraft is positioned in the third sector (4.3) it is understood that the receiver aircraft is located below said appropriate region of the second sector (4.2).
Similarly, the above and below categorized as unsuitable regions in previous example, may be equally positioned both below the suitable area. For instance, this may be the case of the receiver aircraft being an helicopter as middle region ('unsuitable') warns about over-tension of the hose but with no risk for blade impact; while disconnection within the below region may entail both hose over tension and possible collision with rotor blades due to the distance from nominal position of the hose and drogue system.
According to the present invention, the array of references can be a referencing system based on lightening sources or a referencing system with an array of marks at which a pointer device interferes according to the following first and second embodiment, respectively.

First embodiment

Figures 2 and 3a-3c show a first embodiment of a referencing system (1) wherein the array of references comprises an array of light sources (5), particularly the referencing system (1) comprises four light sources (5) as it can be observed in figures 3a-3c. Each light source (5) provides a distinguishable visual indicator for the receiver aircraft by projecting light in a sector (4) (shown in figure 2). Each sector (4) is defined by a predetermined amplitude of projection set by a projection orientation (α_n ), as well as by its amplitude angle (β_n ) according to the position of the desired receiver aircraft with respect to the tanker aircraft.
In this particular example shown in figure 2, the sectors (4.1, 4.2, 4.3, 4.4) partially overlap with adjacent ones so that, supported by the smooth transition of this the partial overlap, it is stablished a readily referring protocol for assisting the receiver aircraft with its relative positioning during in-flight refuelling operation.
It is to be noted that, throughout this first embodiment, each of the sectors (4) defined by the invention corresponds to the beam shape of the associated light source (5). As mentioned, overlaps may give rise to another sector because, at that intermediate position, the receiver aircraft shall perceive both lights on simultaneously, which is indeed distinguishable from the former two lights on separately.
By controlling their amplitude (β_n ) in angle and projection orientation (α_n ), the plurality of sectors (4) comprises a first sector (4.1) with a first amplitude (β₁ ) and a first projection orientation (α₁ ); a second sector (4.2) with a second amplitude (β₂ ) and a second projection orientation (α₂ ); a third sector (4.3) with a third amplitude (β₃ ) and a third projection orientation (α₃ ); and a fourth sector (4.4) with a fourth amplitude (β₄ ) and a fourth projection orientation (α₄ ). Furthermore, in this figure 2 it is shown the hose and drogue system (2) deployed along the region defined by the overlap of the first (4.1), second (4.2) and third (4.3) sectors, this region corresponding to the appropriate region for the refuelling operation between the tanker aircraft and the receiver aircraft.
Additionally, a third variable for tuning-up the light sources (5) may be the light intensity, as it may be dimmed as it is close to the tanker aircraft (see, for instance, sector 4.1). For those risky sectors, the intensity may be higher to account for the over length of the hose (possibly implying over tension) which may cause whipping upon disconnection. In other words, as the receiver aircraft goes away from the tanker aircraft, entailing a hose extension while connected, the light intensity should be high enough so as to warn the pilot about the unsuitability of that sector far away from the nominal position.
Still in figure 2, these light sources (5) are projected from a spot (3) located in the rear part of the tanker aircraft, particularly, in the tail cone of the tanker aircraft, and more particularly in a closed cargo ramp of the tanker. Each light source (5) has a particular distinguishable colour tone (although not appreciable in these figures) so that the receiver aircraft is able to identify his position with respect to the tanker aircraft according to the colour or colours that the receiver aircraft visualizes.
In this particular example, the first sector (4.1) corresponds to the beam of light from a first light source (5.1) of yellow colour tone; the second sector (4.2) corresponds to the beam of light from a second light source (5.2) of dark green colour tone; the third sector (4.3) corresponds to the beam of light from a third light source (5.3) of light green colour tone; and the fourth sector (4.4) corresponds to the beam of light from a four light source (5.4) of red colour tone.
Figures 3a-3c shows respectively a particular visual indicator that the receiver aircraft identifies along his vertical displacement relative to the tanker aircraft.
For example, figure 3a shows a first visual indicator for the receiver aircraft when it is positioned in the region defined by the overlap of all the sectors (4.1-4.4). In this first region the receiver aircraft is positioned below the optimal region of the refuelling operation. Figure 3b shows a second visual indicator for the receiver aircraft when it is positioned in the region defined by the overlap of the first (4.1) and second (4.2) sectors, this region corresponding also to a not optimal region for the refuelling operation. This also happens when the visual indicators corresponds to figure 3c wherein the receiver aircraft is positioned in the first sector (4.1). Both figures 3b-3c corresponds to the casuistry in which the receiver aircraft is positioned out of the optimal location, that is, when the receiver aircraft is positioned above this optimal region for the refuelling operation.
In this first embodiment, the optimal position so that the receiver aircraft performs the refuelling operation, or the disconnection phase, corresponds to the region defined by the overlap of the first (4.1), second (4.2) and third (4.3) sectors.
This former example is for illustrative reasons and actual sectors arrangement may be modified, whether slightly or in major terms, to accommodate to the actual refuelling operation.
Figure 8 shows a particular example of a referencing system (1) comprising six light sources (5). In particular, a first plurality of light sources (5.1) provides a beam of light with a red colour tone and a second plurality of light sources (5.2) provides a beam of light with a white colour tone.
As it will be explained in figure 6, each of these light sources of figure 8 has a beam amplitude between 2.5 and 3.5° in angle. Further, the projection orientation (α_n ) of each light source is gradually displaced 2° in angle, pointing out downwards in left side and gradually shifting up to upwards in right side.

Second embodiment

Figures 4 and 5a-5c show a second embodiment of a referencing system (1) wherein the array of references comprises an array of marks (6) and a pointer device (7) that is distanced from the marks (6), particularly the referencing system (1) comprises six marks (6). The distance of the pointer device (7) from the marks (6) can be adjusted based on the expected in-flight refuelling conditions and the tanker flight parameters.
The visual intersection between the pointer device (7) and the marks (6) provides distinguishable visual indicators corresponding to sectors for the receiver aircraft. Accordingly, this embodiment is based on perspective.
Particularly, figure 4 shows the reference point (8) of the receiver aircraft with respect to the referencing system (1) of a tanker aircraft. That is, the receiver aircraft is able to know its position with respect to the tanker aircraft depending on the visual indicator visualized by this receiver aircraft in combination with the marks (6) and the visually intervention of the pointer device (7).
In this second embodiment, the array of six marks (6) are placed on the spot (3) and are stacked horizontal lines of different colour tones. In a particular example, these horizontal lines are either LED or Infrared lights.
In a further example, these marks (6: 6.1, 6.2, 6.3) are only visible through night-vision goggles, which need to be wore by the pilot of the receiver aircraft.
That is, from the view point (8) of the pilot of the receiver aircraft when close to the tanker aircraft and looking at the spot (3) where references (6, 7) are congregated, the pointer device (7) (e.g. a horizontal suspended bar) intercedes such vision line. Depending on the relative vertical distance of the receiver aircraft, the pilot shall perceive that the pointer device (7) hides some of the marks (6) stacked on the spot (3).
Therefore, if the pointer device (7) hides any of above marks (6.1) (see figure 5a), the pilot acknowledges that he may be flying too low to disconnect. On the other end, if the pilot sees that below marks are hidden (6.3) (see figure 5c), he may be flying too high. The middle situation (see figure 5b), where intermediate marks (6.2) are hidden by the fixed pointer device (7), may be the suitable one for disconnecting the probe.
Depending on the expected flight and receiver aircraft type to be refuelled, the distance and position of the pointer device may be adjusted.
Regardless the embodiment used, whether first or second, in figure 6 it is depicted the nominal position from where the referencing system is sized and adjusted. A C295 tanker aircraft (9) is shown on left side, while two superimposed receiver aircrafts (10) (one being a helicopter) are shown on right side.
One receiver (10), the helicopter, has its probe beneath; while the other aircraft has its probe above the wings. In this representation, both receiver aircrafts (10) are arranged so that the respective probe tip matches.
With this 'general arrangement', and considering that the tanker aircraft (9) is a C295 in the low speed range, the angular range in the X-Z (vertical) plane addresses a scope of 12° in angle (+/- 6° around the nominal position with respect to the horizontal one). As mentioned, for this aircraft couple and taking into account in-flight refueling parameters, it is found appropriate to split the 12° into 6 sectors with 2° intervals between adjacent ones.
Once the probe is connected, the aircraft receiver pilot does not need to look up to another condition but when he intends to disconnect the probe should be in the same relative position that it was originally connected (drogue forces equilibrium, i.e. nominal position) so that the drogue does not skid when disconnecting.
Figure 7 depicts a cargo ramp (11) of a tanker aircraft comprising a referencing system (1) according to the present invention. In the middle, it is shown the hose tunnel outlet (12) from where the hose and drogue system is deployed.
In particular, the referencing system (1) forms part of a wider Vision & Visual Aids subsystem' in charge of providing the tanker and receiver crews with situational awareness to safely perform the refuelling operation.
To achieve this awareness function, the aircraft C295 shown in figures 6 and 7 is equipped in its tail cone (13), preferably in the cargo ramp (11), with dedicated external cameras (14), including a thermal one which will be tested for night operation.
This modified cargo ramp (11) of the tanker aircraft (9) is also configured to provide the receiver aircraft (10) with visual information related to the deployed hose length (X-axis awareness) and related to the relative altitude to the tanker (Z-axis awareness) with a referencing system (1) according to the present invention. To assure their replacement, these dedicated systems may be installed on dedicated fairings of the cargo ramp.
As it was already mentioned, due to the symmetrical hose deployment, no additional aids are necessary for Y-axis awareness.
This C295 cargo ramp platform shown in figure 7 is especially dedicated for very low speed receivers, such as medium helicopters, but also for intermediate speed receivers, such as slow fighters (e.g. F-18). At both refuelling envelopes, other light transport aircraft may be a suitable receiver.

Claims

Tanker aircraft (9) comprising a referencing system (1) for relative positioning a receiver aircraft (10) during in-flight refueling operation via a hose and drogue system (2),
wherein the referencing system (1) comprises an array of references congregated on a spot (3) of the rear part of the tanker aircraft (9), preferably of the tail cone (13) thereof,
wherein the array of references defines a plurality of sectors (4) originated from the spot (3), a sector (4) being defined by its amplitude in angle, wherein,
for each one of these sectors (4), the array of references is configured to provide a distinguishable visual indicator, and
the array of references being adjustable with respect to:
- at least one flight parameter of the tanker aircraft (9), and

- at least one in-flight refueling operation parameter.
Tanker aircraft (9) according to claim 1, wherein the at least one flight parameter of the tanker aircraft (9) comprises tanker aircraft speed and/or its angle of attack.
Tanker aircraft (9) according to any one of claims 1 or 2, wherein the in-flight refueling operation parameter comprises the type of receiver aircraft (10) to be refueled, the sort of drogue, and/or the length of the hose.
Tanker aircraft (9) according to any one of claims 1 to 3, wherein the array of references of the referencing system (1) comprises an array of lights with n light sources (5), n being a natural number greater than or equal to 3,
wherein each light source (5) provides distinguishable visual indicators by projecting light in a sector (4) defined by a predetermined amplitude of projection set by a projection orientation (α_n ), the array of lights being adjustable at least in amplitude (β_n ) and projection orientation (α_n ).
Tanker aircraft (9) according to claim 4, wherein the lights projected by at least two of the n light sources (5) are configured to partially overlap in the respective sectors (4), these at least two sources (5) of light becoming visible at the same time only within the overlapped sectors.
Tanker aircraft (9) according to any one of claims 4 or 5, wherein the n light sources (9) are at least 3 lights, each one emitting light of in any of at least two color tones.
Tanker aircraft (9) according to any one of claims 4 to 6, wherein each sector (4) has an amplitude between 2 to 4° in angle, preferably between 2.5 and 3.5° in angle.
Tanker aircraft (9) according to any one of claims 4 to 7, wherein the projection orientation (α_n ) of each light source is gradually displaced 2° in angle.
Tanker aircraft (9) according to any one of claims 1 to 3, wherein the array of references of the referencing system (1) comprises an array of n marks (6), n being a natural number greater than or equal to 3, and a pointer device (7) distanced from the marks (6),
wherein each mark (6) provides a distinguishable visual indicator in cooperation with the pointer device (7) for a different sector (4) in such a way that the pointer device (7) visually intervenes a different mark (6) on the spot (3) for a different sector (4).
Tanker aircraft (9) according to claim 9, wherein the array of references are adjustable by changing the distance of the pointer device (7) from the marks (6).
Tanker aircraft (9) according to any one of claims 9 or 10, wherein the array of n marks (6) on the spot (3) are stacked horizontal lines of different color tones.
Method for assisting on relative positioning a receiver aircraft (10) during in-flight refueling operation of tanker aircraft (9) according to any one of claims 1 to 11, wherein the array of references of the tanker aircraft (9) has been previously adjusted with respect to at least one flight parameter thereof, and at least one in-flight refueling operation parameter;
wherein the method comprises the following steps:
a) deploying the hose and drogue system (2) by the tanker aircraft (9) during the in-flight refueling operation, and

b) detecting by the tanker aircraft (9) that a probe of a receiver aircraft (10) to be refueled is coupled, saving the sector (4) from the spot (3) at which the coupling occurs.
Method for assisting on relative positioning a receiver aircraft (10) during in-flight refueling operation according to claim 12, wherein the tanker aircraft (9) is according to any one of claims 4 to 8, and
wherein the array of references of the tanker aircraft (9) has been previously adjusted on-ground so that the adjustment of the distinguishable visual indicators comprises projecting light from the n sources (5) of light in sectors (4), further adjusting their predetermined projection amplitude (β_n ) and projection orientation (α_n ) based on the at least one flight parameter of the tanker aircraft (9) during the following in-flight refueling operation, and at least one in-flight refueling operation parameter.
Method for assisting on relative positioning a receiver aircraft (10) during in-flight refueling operation according to claim 12, wherein the tanker aircraft (9) is according to any one of claims 9 to 11, and
wherein the array of references of the tanker aircraft (9) has been previously adjusted on-ground so that the adjustment of the distinguishable visual indicators comprises changing the distance of the pointer device (7) from the marks (6) based on the at least one flight parameter of the tanker aircraft (9) during the following in-flight refueling operation, and at least one in-flight refueling operation parameter.
Method for uncoupling the hose and drogue system of a tanker aircraft (9) according to any one of claims 1 to 11 from a probe of a receiver aircraft (10) during in-flight refueling operation;
wherein the referencing system (1) defines at least 3 sectors (4) corresponding with different altitudes of the receiver aircraft (10) during the in-flight refueling operation, the at least 3 sectors (4) categorized as upper, suitable, and lower sectors, respectively, and wherein at the suitable sector, the tension of the deployed hose is minimum;
wherein the method comprises:
i. positioning the receiver aircraft (10) within the suitable sector, and

ii. uncoupling the hose and drogue system (2) by the tanker aircraft (9) from the probe of the receiver aircraft (10).